elf/dl-load.h

   1 /* Map in a shared object's segments from the file.
   2    Copyright (C) 1995-2022 Free Software Foundation, Inc.
   3    Copyright The GNU Toolchain Authors.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #ifndef _DL_LOAD_H
  21 #define _DL_LOAD_H      1
  22
  23 #include <link.h>
  24 #include <sys/mman.h>
  25
  26
  27 /* On some systems, no flag bits are given to specify file mapping.  */
  28 #ifndef MAP_FILE
  29 # define MAP_FILE       0
  30 #endif
  31
  32 /* The right way to map in the shared library files is MAP_COPY, which
  33    makes a virtual copy of the data at the time of the mmap call; this
  34    guarantees the mapped pages will be consistent even if the file is
  35    overwritten.  Some losing VM systems like Linux's lack MAP_COPY.  All we
  36    get is MAP_PRIVATE, which copies each page when it is modified; this
  37    means if the file is overwritten, we may at some point get some pages
  38    from the new version after starting with pages from the old version.
  39
  40    To make up for the lack and avoid the overwriting problem,
  41    what Linux does have is MAP_DENYWRITE.  This prevents anyone
  42    from modifying the file while we have it mapped.  */
  43 #ifndef MAP_COPY
  44 # ifdef MAP_DENYWRITE
  45 #  define MAP_COPY      (MAP_PRIVATE | MAP_DENYWRITE)
  46 # else
  47 #  define MAP_COPY      MAP_PRIVATE
  48 # endif
  49 #endif
  50
  51 /* Some systems link their relocatable objects for another base address
  52    than 0.  We want to know the base address for these such that we can
  53    subtract this address from the segment addresses during mapping.
  54    This results in a more efficient address space usage.  Defaults to
  55    zero for almost all systems.  */
  56 #ifndef MAP_BASE_ADDR
  57 # define MAP_BASE_ADDR(l)       0
  58 #endif
  59
  60
  61 /* Handle situations where we have a preferred location in memory for
  62    the shared objects.  */
  63 #ifdef ELF_PREFERRED_ADDRESS_DATA
  64 ELF_PREFERRED_ADDRESS_DATA;
  65 #endif
  66 #ifndef ELF_PREFERRED_ADDRESS
  67 # define ELF_PREFERRED_ADDRESS(loader, maplength, mapstartpref) (mapstartpref)
  68 #endif
  69 #ifndef ELF_FIXED_ADDRESS
  70 # define ELF_FIXED_ADDRESS(loader, mapstart) ((void) 0)
  71 #endif
  72
  73
  74 /* This structure describes one PT_LOAD command.
  75    Its details have been expanded out and converted.  */
  76 struct loadcmd
  77 {
  78   ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
  79   ElfW(Off) mapoff;
  80   int prot;                             /* PROT_* bits.  */
  81 };
  82
  83
  84 /* This is a subroutine of _dl_map_segments.  It should be called for each
  85    load command, some time after L->l_addr has been set correctly.  It is
  86    responsible for setting up the l_text_end and l_phdr fields.  */
  87 static __always_inline void
  88 _dl_postprocess_loadcmd (struct link_map *l, const ElfW(Ehdr) *header,
  89                          const struct loadcmd *c)
  90 {
  91   if (c->prot & PROT_EXEC)
  92     l->l_text_end = l->l_addr + c->mapend;
  93
  94   if (l->l_phdr == 0
  95       && c->mapoff <= header->e_phoff
  96       && ((size_t) (c->mapend - c->mapstart + c->mapoff)
  97           >= header->e_phoff + header->e_phnum * sizeof (ElfW(Phdr))))
  98     /* Found the program header in this segment.  */
  99     l->l_phdr = (void *) (uintptr_t) (c->mapstart + header->e_phoff
 100                                       - c->mapoff);
 101 }
 102
 103
 104 /* This is a subroutine of _dl_map_object_from_fd.  It is responsible
 105    for filling in several fields in *L: l_map_start, l_map_end, l_addr,
 106    l_contiguous, l_text_end, l_phdr.  On successful return, all the
 107    segments are mapped (or copied, or whatever) from the file into their
 108    final places in the address space, with the correct page permissions,
 109    and any bss-like regions already zeroed.  It returns a null pointer
 110    on success, or an error message string (to be translated) on error
 111    (having also set errno).
 112
 113    The file <dl-map-segments.h> defines this function.  The canonical
 114    implementation in elf/dl-map-segments.h might be replaced by a sysdeps
 115    version.  */
 116 static const char *_dl_map_segments (struct link_map *l, int fd,
 117                                      const ElfW(Ehdr) *header, int type,
 118                                      const struct loadcmd loadcmds[],
 119                                      size_t nloadcmds,
 120                                      const size_t maplength,
 121                                      bool has_holes,
 122                                      struct link_map *loader);
 123
 124 /* All the error message strings _dl_map_segments might return are
 125    listed here so that different implementations in different sysdeps
 126    dl-map-segments.h files all use consistent strings that are
 127    guaranteed to have translations.  */
 128 #define DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT \
 129   N_("failed to map segment from shared object")
 130 #define DL_MAP_SEGMENTS_ERROR_MPROTECT \
 131   N_("cannot change memory protections")
 132 #define DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL \
 133   N_("cannot map zero-fill pages")
 134
 135
 136 #endif  /* dl-load.h */